The 81st Regiment Illinois Volunteer Infantry was an infantry regiment that served in the Union Army during the American Civil War.

The 81st Illinois Infantry was organized at Anna, Illinois and mustered into Federal service on August 21, 1862.

The regiment was mustered out on August 5, 1865.

The regiment suffered 8 officers and 66 enlisted men who were killed in action or who died of their wounds and 3 officers and 292 enlisted men who died of disease, for a total of 369 fatalities.

This article about a specific military unit of the American Civil War is a stub.